It is known to charge certain types of batteries, such as lithium-ion batteries, using an approach that is commonly referred to as constant current/constant voltage charging. Constant current/constant voltage charging typically involves charging a battery by first providing a constant current thereto and later charging the battery by providing a constant voltage.
One of the reasons that the constant current/constant voltage approach is used is that as the charge stored by the battery approaches full capacity, it may be problematic to continue to provide a constant current as the capacity of the battery to absorb current is reduced. For example, if a constant current is provided to the battery past a safe threshold, the battery may be damaged, or alternatively, the charging circuit may be damaged.
One type of constant current/constant voltage battery charger circuit is discussed, for example, in U.S. Pat. No. 6,522,118 to Barcelo, et al. The circuits discussed in Barcelo include a constant current loop and a constant voltage loop connected to a priority circuit which determine which of the two loops to use in charging the battery. For example, FIG. 3 of Barcelo shows a constant current loop with a first amplifier and a first voltage controlled current source coupled to a load resistor. The circuit of FIG. 3 also includes a constant voltage loop with a second amplifier and a second voltage controlled current source coupled to the battery. Both of the loops are connected to the priority circuit, which selects, for example, a lower of the two amplifier voltages to be provided to the voltage controlled current sources.